The first use of ozone was in 1906 in France. It was used as an oxidizing
agent to disinfect water. After 70 years of advancement in wastewater treatment
technology, the synergistic effects of UV light, ozone, and hydrogen peroxide
were finally discovered in 1976. During the years before this finding,
technology was created combining ultraviolet light (UV) with ozone and
UV with hydrogen peroxide. Following the discovery of treatment technology
combining these three components, Ultrox International of Santa Ana, California
built a system to treat wastewater using UV, ozone, and peroxide in 1984
(1).

UV/Ozone/Peroxide treatment is an ultraviolet radiation and oxidation
technology. As the name implies UV/Ozone/Peroxide treatment is comprised
of three individual components: ultraviolet radiation, ozone gas, and hydrogen
peroxide solution. The components together use radiation and chemical oxidation
to disinfect and destroy a wide range of contaminants. To understand how
the UV/Ozone/Peroxide treatment works it is necessary to understand the
individual components. Together ozone and hydrogen peroxide comprise the
chemical oxidation aspect of UV/Ozone/Peroxide treatment while ultraviolet
light makes up the radiation aspect.

CHEMICAL OXIDATION

Chemical oxidation is a process by which compounds, such as waste products
are oxidized to a more environmentally benign state. Waste products that
can be destroyed by oxidation include organic molecules, chlorinated VOCs,
mercaptans, phenols, and some inorganics. Cyanide (NaCN) is one such product,
which can be oxidized in the presence of ozone to a safer state (2):

O3 + NaCN --> NaCNO + O2

Oxidation and reduction equations occur in pairs to make up an overall
redox equation. The governing factor behind oxidation is the standard electrode
potentials of the chemicals involved. Chemicals, which have high positive
values for electrode potential, such as hydrogen peroxide and ozone, spontaneously
react with other chemicals. Ozone is commonly used in water and wastewater
applications as a disinfectant because it is a powerful oxidant, and reacts
with most toxic organics. Ozone reacts with organic molecules in many ways:
inserting an oxygen into a benzene ring, breaking double bonds to form
aldehydes and ketones, reacting with alcohol to form organic acids (2).

Hydrogen peroxide is used to treat liquid and solid hazardous wastes
because it readily reacts with organic chemicals to form carbon dioxide
and water. Chemicals that are reactive with hydrogen peroxide are as follows:
nitriles, aldehydes, alcohols, amines, metals, alkylboranes, azo-compounds,
cyanides, phenols, sulfides, and chromium (1). But, it is not necessarily
hydrogen peroxide or ozone which reacts with a reducing agent. Ozone decomposes
in a solution of water and hydrogen peroxide decomposes in the presence
of an iron catalyst to create a large number of hydroxyl radicals (OH-).
It is the hydroxyl radicals that react with compounds at a much higher
rate than the parent compound. Another way to enhance the oxidation reactions
for both ozone and hydrogen peroxide is through the use of ultraviolet
radiation.

RADIATION

Radiation is a process by which energy is transferred from one location
to another. One such form of radiation is ultraviolet light. Ultraviolet
light is often used as a disinfectant in water and wastewater treatment.
Radiation in high doses can permanently damage the building blocks of life.
It is with this method that ultraviolet light is used to kill microorganisms
and disinfect water. Ultraviolet radiation is powerful enough to break
many covalent bonds. Alone it can degrade PCBs, dioxins, polyaromatic compounds,
and BTEX (1). UV light has another affect; it enhances chemical oxidation.
The way ultraviolet light enhances chemical oxidation is somewhat of mystery.
One theory is that organic compounds absorb light energy at visible or
ultraviolet wavelengths and as a result are easier to destroy. In short,
UV/Ozone/Peroxide treatment is combination of the above technologies. In
combining several oxidation methods with a source of radiation energy,
the limitations of the individual components are reduced.

A full scale UV/Ozone/Peroxide treatment system treats contaminated
groundwater, industrial wastewater, and leachates containing chemicals
such as: halogenated solvents, phenol, pentachlorophenol, pesticides, PCB's,
explosives, BTEX, MTBE, and many other organic compounds. The UV radiation
and oxidation system consists of a UV/Oxidation reactor, an air compressor
with an ozone generator module, and a hydrogen peroxide feed system. A
common UV/Ozone/Peroxide process is shown below in Figure 1(3):

Figure 1: UV/Ozone/Peroxide Process Schematic

ADVANTAGES

The advantages of a treatment process using ultraviolet light, ozone,
and hydrogen peroxide are numerous. The first one involves the actual treatment
technology. A UV/Ozone/Peroxide system is a destruction process, and the
final products are only carbon dioxide, water, and inert salts (4,5). Therefore,
the process residuals do not require any additional treatment, as they
might in conventional systems.

In the UV/Ozone/Peroxide process, ozone is used as an oxidant, instead
of the more conventional use of chlorine. Ozone is a better disinfectant
than chlorine and is not known to produce toxic or mutagenic substances
(1). Also, because ozone must be generated on site and used immediately,
no storage area is required for the oxidant (6).

The costs involved with the UV/Ozone/Peroxide process are lower than
the costs for a system utilizing only ultraviolet light and ozone, because
the addition of hydrogen peroxide allows the use of a smaller ozone generator
and less oxidants (1). Also, the residence times needed to decrease the
concentration of a contaminant to a certain level are lower for the UV/Ozone/Peroxide
system than for ozone alone, UV/Ozone, or UV/Peroxide processes (2).

The final advantage of this treatment technology is the wide variety
of contaminants and concentrations that can be treated. The limitations
of ultraviolet light, ozone, and hydrogen peroxide alone are overcome by
combining the three constituents. Finally, the oxidants and the Ultrox
International system are becoming readily available (1,4).

DISADVANTAGES

There are still a few limitations and dangers involved with the UV/Ozone/Peroxide
treatment technology. High turbidity, solid particles, and heavy metal
ions in the aqueous stream are all interferences that reduce the effectiveness
of the treatment (4). Because these substances must be removed to ensure
good treatment, the aqueous stream may need pretreatment.

Unfortunately, the equipment needed for this new treatment process can
be expensive and require a large amount of space. The energy required for
the process is high resulting in large costs (1,4). Also, capital costs
are higher for the UV/Ozone/Peroxide system than for conventional systems,
but operating costs are lower (1). Ozone can also be costly, because it
must be generated and immediately applied at the treatment location (2).
Finally, large areas are needed for the many ultraviolet lamps required
in this process (5).

Each of the constituents in the UV/Ozone/Peroxide process has dangers.
Ozone is explosive, toxic, and an irritant to the skin, eyes, respiratory
tract, and mucous membrane (7). Hydrogen peroxide is an irritant, can cause
chemical burns, and is an explosive hazard (1). Ultraviolet light can burn
unprotected skin and the mercury in UV lamps can damage the central nervous
system, along with inflaming the nose and throat area (4).

Ozone is also a significant air pollutant and monitoring must be completed
to ensure that ozone levels are not exceeding regulatory concentrations
(2). Lastly, the UV/Ozone/Peroxide process mechanisms are still not totally
understood.

CASE STUDY(8)

In developing any new treatment technology, case studies are a must
in determining their capability of treating a contaminant. One of the first
case studies for UV/Ozone/Peroxide treatment was done for the US Department
of Energy Kansas City Plant (KCP) in Kansas City, Missouri. The main source
of contamination was volatile organic compounds (VOCs) and the identified
surrogate chemicals were PCE, TCE, 1,2-DCEs and Vinyl Chloride. The field
application used was a pump and treat system that extracted contaminated
groundwater for remediation. The remediation treatment was through advanced
oxidation processes (AOP), using a UV/Ozone/Peroxide treatment system,
which ran from May 1988 to May 1993. When the UV/Ozone/Peroxide system
was initiated in 1988, it was one of the first full-scale operating AOP
of its kind. For the first 4 years, close monitoring of the treatment system
to develop pilot studies to verify this new treatment was performed for
regulators to see. At the end of the 4 years, an improved UV/Peroxide system
was implemented (currently on going) from the previous 4-year pilot study
and is shown below in Figure 2:

Figure 2: Modified UV/Peroxide Treatment Schematic

The results below illustrate the effectiveness of the treatment at the
KCP site:

Table 1: Final Concentrations of the KCP UV/Ozone/Peroxide Treatment
Process

Treatment Process

Contaminant

Influent Contaminant Concentration, m
g/l

Effluent Contaminant Concentration, m
g/l

Percent Removal

Percent Detected in Ambient Air

Percent Detected in Sewer Discharge

Initial UV/O3/H2O2

VOCs

-

-

@ 94.6%

@ 3.7%

@ 1.7%

Modified UV/ H2O2

VOCs

-

-

>99.95%

0.00 %

<0.05%

Modified UV/ /H2O2

PCB

0.3

0.0

100 %

0.00%

0.00%

Based on these results the use of the UV/Ozone/Peroxide, especially
the modified UV/Peroxide system, proved an effective process for removing
and containing VOC contamination in the groundwater. The system was designed
to treat 30,000 m g/l and the average influent
was 25,00 m g/l. Along with the high contaminant
removal, the system design conditions were met. The modified UV/Peroxide
process replaced the UV/Ozone/Peroxide system,because the initial
system, containing ozone, required lots of maintenance on the ozone generator
and the delivery system. Ozone leaks were discovered (causing downtime)
and the residual ozone proved to be corrosive in the reaction chamber.
Several other improvements were made to the initial UV/Ozone/Peroxide process
because serious downtime was encountered for acid cleaning of the filters,
UV lamp sheathes, and ozone sparger tubes. The modified system took this
into account and added a pH adjustment before the UV/Peroxide treatment
and therefore lessened the chance of fouling due to the oxidation of organics.

Overall, the research procedure was deemed very useful. An initial design
was tested, and based on the results a modified system was implemented,
which is the whole basis of research. The initial UV/Ozone/Peroxide demonstration
system served as a stepping stone in developing the modified UV/Peroxide
processand clearly treated the saturated hydrocarbon contamination.

As with most ex-situ treatment processes, especially pump and treat
methods, much of the VOC mass is removed from the subsurface and treated
with UV/Peroxide or UV/Ozone/Peroxide, but there is still some in-situ
groundwater VOC concentrations that will remain untreated. This therefore
limits most ultraviolet treatment systems, unless improved extraction procedures
are utilized.

FUTURE CONSIDERATIONS

The future of this treatment technology includes continuing to learn
more about the process and how to improve it. Higher intensity ultraviolet
lamps are already being produced to reduce the space and cost requirements
for this process (5). Another innovation currently being studied is a way
to reduce the number of solid particles in the aqueous stream, so the amount
of UV light reaching the particles is greater. An electron-beam accelerator
can be used to "zap" the aqueous stream and oxidize organic contaminants
to form harmless substances, like carbon dioxide and salts (8). The UV/Ozone/Peroxide
treatment technology is still new and advances are constantly being discovered
to improve the process.